Process for preparing diesel fuels using vegetable oils or fatty acid derivatives

ABSTRACT

A process for preparing fuels, such as diesel fuels or jet fuels, by hydrotreating vegetable oils or fatty acid derivatives that may be applied to existing equipment for treating fossil fuels. The process comprises feeding hydrotreating a combined oxygenate feed stream, such as FAME, and a hydrocarbon feed stream until not more than 86 wt % of the esters in the oxygenate feed stream are converted to hydrocarbons, and optionally further hydrotreating the product stream within at least a second hydrotreatment reaction zone until at least 90 wt % of the esters in the oxygenate feed stream are converted to hydrocarbons, before removing and separating a hydrocarbon stream suitable for use as fuel.

This application claims the benefit of U.S. Provisional Application61/268,460 filed Jun. 12, 2009.

FIELD OF THE INVENTION

This invention relates to a process for preparing fuels such as dieselfuels, heating oil, or jet fuels, using vegetable oils or fatty acidderivatives derived from them. In particular it relates to a process forhydrotreating vegetable oils or fatty acid derivatives that may beapplied to existing equipment for treating fossil fuels.

BACKGROUND OF THE INVENTION

Environmental interests and an increasing worldwide demand for energyhave encouraged energy producers to investigate renewable energysources, including biofuels. Biofuel is obtained from biologicalmaterial that is living or relatively recently lifeless, in contrast tofossil fuels (also referred to as mineral fuels) which are derived fromancient biological material. There is particularly interest in biofuelswhere, as in Europe, regulatory requirements have been or will beintroduced that will require increased use of biofuels for motorvehicles, principally by blending with mineral fuels.

Biofuels are typically made from sugars, starches, vegetable oils, oranimal fats using conventional technology from basic feedstocks, such asseeds, often referred to as bio-feeds. For example, wheat can providestarch for fermentation into bioethanol, while oil-containing seeds suchas sunflower seeds provide vegetable oil that can be used in biodiesel.

Some diesel engines are compatible with pure biodiesel, without the needfor modifications. But generally biodiesel is mixed with mineral dieselso that it may be used in a wider range of diesel engines. Currentlyvehicle manufacturers recommend use of fuel containing up to 15%biodiesel blended with mineral diesel.

The conventional approach for converting vegetable oils or other fattyacid derivatives into liquid fuels in the diesel boiling range is by atransesterification reaction with an alcohol, typically methanol, in thepresence of catalysts, normally a base catalyst such as sodiumhydroxide. The product obtained is typically a fatty acid alkyl ester,most commonly fatty acid methyl ester (known as FAME). While FAME hasmany desirable qualities, such as high cetane and its perceivedenvironmental benefit, it has poor cold flow relative to mineral dieselbecause of its straight hydrocarbon chain. It also has lower stabilitybecause of the presence of ester moieties and unsaturated carbon-carbonbonds.

Hydrogenation methods are also known to convert vegetable oils or otherfatty acid derivatives to hydrocarbon liquids in the diesel boilingrange. These methods remove undesirable oxygen by hydrodeoxygenation toproduce water, hydrodecarbonylation to produce CO, orhydrodecarboxylation to produce CO₂. In hydrodeoxygenation, unsaturatedcarbon-carbon bonds present in feed molecules are saturated(hydrogenated) before deoxygenation. Compared to transesterification,this type of hydrotreating has the practical advantage that it may bepracticed in a refinery utilizing existing infrastructure. This reducesthe need for investment and provides potential for operating on a scalethat is more likely to be economical.

There are methods, developed by UOP (EcoFining) and Neste, which processtriglycerides, such as found in vegetable oils, in a stand-alone manner.For instance, PCT Publication No. WO 2008/020048 describes a process forcoprocessing triglycerides with heavy vacuum oil in single or multiplereactors, and partial hydrogenation of oxygenated hydrocarbon compoundssuch as glycerol is disclosed as being more desirable from theperspective of hydrogen consumption. PCT Publication No. WO 2008/012415describes a process for the catalytic hydrotreatment of a feedstockderived from petroleum, of the gasoil type, in at least one fixed bedhydrotreatment reactor, wherein up to about 30% by weight of vegetableoils and/or animal fats are incorporated into the feedstock, and thereactor is operated in a single pass without recycle.

European Patent No. EP 1911735 describes co-hydrogenation of acarboxylic acid and/or derivative with a hydrocarbon stream from arefinery, as a retrofit. CoMo or NiMo catalysts are disclosed. It isstated that conditions are maintained in the reactor such that almostcomplete conversion of the carboxylic acid and/or ester is achieved,that is, greater than 90% conversion and preferably greater than 95%conversion. The product is described as suitable for use as or with adiesel fuel.

PCT Publication No. WO 2008/040973 describes a process, which issuitable as a retrofit, in which a mixed feed of carboxylic acid and/orderivatives including esters, and a refinery process stream, such as adiesel fuel, are hydrodeoxygenated or simultaneously hydrodesulfurizedand hydrodeoxygenated. The catalyst may be Ni or Co in combination withMo. The process produces a product which is described as suitable foruse as diesel, gasoline or aviation fuel. It is stated that, under thedescribed conditions, conversions of greater than 90% of the co-fedcarboxylic acid and/or derivatives are typical and usually greater than95% is achieved.

PCT Publication No. WO 2007/138254 describes a process in which in afirst stage a hydrocarbon process stream, which may be a middledistillate, is hydrogenated and then fed with a carboxylic acid and/orester to a second hydrogenation stage. The final product may be dieselfuel, and the benefits are said to be reduced exotherm, improved dieselyield, reduced fouling, reduced coking, and reduced residual olefinsand/or heteroatoms. Mention is made of an alternative process in whichan untreated hydrocarbon process stream is fed with the ester.Conditions in the second reactor are said to be the same as the first,and NiMo and CoMo are described as preferred catalysts for the firstreactor. It is stated that conditions are maintained in the reactor suchthat almost complete conversion of the carboxylic acid and/or ester isachieved, that is greater than 90% conversion and preferably greaterthan 95% conversion.

Unlike conventional distillate hydrodesulfurization, directhydrotreating of vegetable oils or animal fats requires a relativelyhigh amount of hydrogen and is generally accompanied by a large amountof heat release, which requires extremely careful control. Otherwiseundesirable side reactions, such as cracking, polymerization, andaromatization may result. Additionally, co-processing triglycerides andFAME over CoMo catalysts has shown a hydrodesulfurization debit.Therefore, there is a need for an improved hydrotreating process forvegetable oils and animal fats, and preferably that may be performed inexisting equipment for treating mineral fuels.

SUMMARY OF THE INVENTION

According to this invention, there is provided a process for producing ahydrocarbon stream suitable for use as fuel from carboxylic esters,which process comprises the steps of:

-   -   a) feeding to a hydrotreatment reaction zone (i) an oxygenate        feed stream comprising one or more methyl or ethyl esters of        carboxylic acids, and (ii) a hydrocarbon feed stream;    -   b) contacting the feed streams within the hydrotreatment        reaction zone with a gas comprising hydrogen under        hydrotreatment conditions until not more than 86 wt % of the        esters in the oxygenate feed stream are converted to        hydrocarbons;    -   c) removing a hydrotreated product stream; and    -   d) separating from the hydrotreated product stream a hydrocarbon        product stream suitable for use as fuel.

According to another aspect of the invention, the hydrotreated productstream obtained from the hydrotreatment reaction zone in step b) abovecan be further hydrotreated in at least a second hydrotreatment reactionzone by contacting with hydrogen under hydrotreatment conditions untilat least 90 wt % (preferably at least 95 wt %, more preferably at least99 wt %) of the esters in the oxygenate feed stream are converted tohydrocarbons; and in step c) the hydrotreated product stream can beremoved from the second hydrotreatment reaction zone. This aspect of theinvention may be applied to a broader range of carboxylic esterfeedstocks.

Thus, in a second embodiment the invention comprises:

-   -   a) feeding to a first hydrotreatment reaction zone an oxygenate        feed stream comprising one or more esters, particularly alkyl        esters, of carboxylic acids, and a hydrocarbon feed stream;    -   b) (i) contacting the feed streams within the first        hydrotreatment reaction zone with a gas comprising hydrogen        under hydrotreatment conditions until not more than 86% of the        esters in the oxygenate feed stream are converted by        hydrodeoxygenation to hydrocarbons,        -   (ii) removing from the first hydrotreatment reaction zone a            first hydrotreated product stream,        -   (iii) contacting the first hydrotreated product stream            within at least a second hydrotreatment reaction zone with a            gas comprising hydrogen under hydrotreatment conditions            until at least 90 wt % (preferably at least 95 wt %, more            preferably at least 99 wt %) of the esters in the oxygenate            feed stream are converted to hydrocarbons;    -   c) removing from the second hydrotreatment reaction zone a        second hydrotreated product stream; and    -   d) separating from the second hydrotreated product stream a        hydrocarbon stream suitable for use as fuel.

As used herein, the phrase “alkyl ester”, with reference to esters ofcarboxylic acids treated according to the second embodiment, should beunderstood to mean a straight or branched hydrocarbon having from 1 to24 (preferably from 1 to 18, more preferably from 1 to 12, for examplefrom 1 to 8) carbon atoms attached via an ester bond to a carboxylatemoiety. For clarity, though a preferred alkyl ester of a carboxylic acidincludes fatty acid esters such as FAME, there is no requirement thatthe alkyl esters of carboxylic acids be characterized as “fatty acid”esters in order to be useful in the second embodiment of the invention.

The oxygenate feed stream for the second embodiment may be derived frombiomass by a transesterification reaction with an appropriate alcohol,that is a C₁ to C₂₄ alcohol, in the presence of catalysts, normally abase catalyst such as sodium hydroxide, to obtain a fatty acid alkylester (e.g., where the alkyl group is a methyl and/or ethyl group). Theoxygenate feed stream may contain esters of carboxylic acids which aresaturated or unsaturated, with unsaturated esters containing one ormore, typically one, two or three, olefinic groups per molecule.Examples of unsaturated esters include esters of oleic, linoleic,palmitic, and stearic acid. A preferred oxygenate feed stream for thesecond embodiment comprises one or more methyl or ethyl esters ofcarboxylic acids.

Whether used in the first or second embodiment, an oxygenate feed streamcomprising one or more methyl or ethyl esters of carboxylic acids may bederived from biomass by a transesterification reaction with theappropriate alcohol, that is methanol and/or ethanol. Preferably, theoxygenate feed stream comprises fatty acid methyl ester (FAME),although, where a lower net greenhouse gas emissions effect process isof increased importance, processing of fatty acid ethyl esters (FAEE)can be advantageous (due to the use of ethanol instead of methanol as atransesterification agent).

The processes of the invention provide for the manufacture ofhydrocarbons for fuels that have relatively low (e.g., trace) amounts ofsulfur and have converted oxygenates, and especially converted FAME, bycoprocessing the oxygenates with a hydrocarbon feed stream.

The conversion of the esters in the oxygenate feed stream tohydrocarbons may be the result of hydrodeoxygenation to form water and ahydrocarbon, hydrodecarboxylation to produce CO and a hydrocarbon,and/or hydrodecarboxylation to produce CO₂ and a hydrocarbon. Variationsin the conditions such as temperature and hydrogen partial pressure canoften dictate which mechanism(s) occur.

The application of the invention to the conversion of esters such asFAME may provide particular advantages over coprocessing of biofuelscontaining predominantly non-transesterified vegetable oils with ahydrocarbon feed stream; a non-exclusive list of these advantages caninclude, but is not necessarily limited to:

-   -   1. Esterified carboxylic (fatty) acids such as FAME are        inherently more thermally stable than vegetable oils, which can        result in:        -   a) improved processability;        -   b) less gas make from cracking; and/or        -   c) being able to process at higher temperatures, such as            those encountered in cat feed hydrotreaters and hydrocracker            pretreaters, and under the more severe conditions near the            end of a catalyst run, which allows longer run lengths.    -   2. Mild hydrotreatment conditions, such as those found in some        distillate hydrofiners, may not result in complete conversion of        vegetable oil, and unconverted vegetable oil may cause fouling        downstream as it tends to have a high molecular weight. If        esterified carboxylic (fatty) acids such as FAME are not        completely hydrodeoxygenated, because they are typically in the        same molecular weight range as diesel, it should not adversely        impact the diesel pool or give rise to significant fouling.    -   3. More esterified carboxylic (fatty) acids such as FAME can be        processed in a unit as compared to vegetable oil, or conversely        a unit to process a certain volume of such esterified carboxylic        (fatty) acids would be smaller than a unit to process the same        amount of vegetable oil.    -   4. Esterified carboxylic (fatty) acids such as FAME tend to be        smaller molecules, and therefore less resistant to diffusion,        than vegetable oils. In a diffusion limited environment such as        that encountered in a hydrotreatment reactor, esterified        carboxylic (fatty) acids such as FAME are preferred for one or        more of the following reasons:        -   a. fewer hot spots can tend to develop in the catalyst,            permitting        -   b. a higher temperature in the reactor;        -   c. less coking can tend to occur; and        -   d. better catalyst utilization.

In the embodiment of the invention using two hydrotreatment reactionzones, the zones may be present in separate reactors or as distinctzones within a single reactor; this embodiment may have a number offurther advantages. For example, by operating in two separate stages ofhydrotreatment, heat can be removed between reactors using heatexchangers or quench gas, which can facilitate better control of heatrelease from the process. Additionally or alternately, it may bepossible to separate out at least a portion of light ends, such as CO,CO₂, or water, from the first hydrotreated product (preferably at least10% by weight, more preferably at least 30% by weight, and mostpreferably at least 50% by weight, based on the weight of light ends inthe first hydrotreated product) before entering the second reactionzone, which may improve catalyst activity and cycle length.

In certain cases, processing biofeeds can reduce the activity ofhydrodesulfurization catalysts relative to processing conventionalmineral streams from a refinery. The processes of the invention canadvantageously make it easier to manage this loss of activity, asconditions in the second reaction zone can compensate for any additionalsulfur passing through from the first reaction zone.

Additionally, as the olefin saturation and alkyl (methyl) removal aretypically exothermic, one could use the heat of reaction from the firstreaction zone to preheat the liquid to the necessary inlet temperatureof the second reaction zone.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic representation of apparatus for carrying outan embodiment of the process of the invention with two hydrotreatmentreaction zones situated in two separate reactors. This is one of manypossible configurations of apparatus for carrying out the process of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One of the advantages of the processes of the invention is that theprocess may be carried out in conventional hydrotreatment facilitiesfound in a refinery. Thus, the or each hydrotreatment reaction zone maybe, for example, a diesel hydrotreater, cat feed hydrotreater (CFHT), orhydrocracker-hydrotreater. This may enable the process to be a retrofitinto existing refinery facilities, which reduces investment costs inequipment. The embodiment of the invention that uses a two stagetreatment is particularly beneficial for a retrofit, as it enables moreconstrained existing units to be employed.

The oxygenate feed stream may be derived from biomass, and is preferablyderived from plant oils such as rapeseed oil, palm oil, peanut oil,canola oil, sunflower oil, tall oil, corn oil, soybean oil, olive oil,jatropha oil, jojoba oil, and the like, and combinations thereof. It mayadditionally or alternately be derived from animal oils and fats, suchas fish oil, lard, tallow, chicken fat, milk products, and the like, andcombinations thereof, and/or from algae. Waste oils such as used cookingoils can also be used.

A typical feed stream contains alkyl (preferably methyl and/or ethyl,for example methyl) esters of carboxylic acids such as methyl esters ofsaturated acids (typically having from 8 to 36 carbons attached to thecarboxylate carbon, preferably from 10 to 26 carbons, for example from14 to 22 carbons), which may contain one more unsaturated carbon-carbonbonds. Preferred FAME feedstreams can contain:

-   -   Methyl ester of C₁₈ saturated acid    -   Methyl ester of C₁₈ acid with 1 olefin bond    -   Methyl ester of C₁₈ acid with 2 olefin bonds    -   Methyl ester of C₁₈ acid with 3 olefin bonds    -   Methyl ester of C₂₀ saturated acid

The hydrocarbon feed stream may be a refinery process stream or asynthetic stream such as may be derived from a Fischer-Tropschsynthesis. The hydrocarbon feed stream may be already suitable for useas a fuel, such as gasoline, diesel or aviation fuel. It mayalternatively be a stream obtained from the refinery which requiresfurther processing to be suitable for use as fuel. For example, it maybe a stream such as a distillate, and in particular a straight runmiddle distillate, a light or heavy gas oil fraction or a catalyticallycracked vacuum gas oil. Mixtures of refinery streams and/or syntheticstreams may also be used. The hydrocarbon feed stream may containheteroatom-containing compounds such as sulfur-containing compounds. Thehydrotreatments of the process of the invention can, in preferredembodiments, simultaneously desulfurize the hydrocarbon feed whenconverting the oxygenate feed to hydrocarbons.

The relative proportions of the oxygenate feed and the hydrocarbon feedstreams will generally be dictated by the amount of biofuel desired inthe ultimate (e.g., diesel fuel) product. The oxygenate feed typicallycomprises from 0.5 to 50 wt % of the combined feed to the hydrotreatmentreaction zone in step a), preferably from 1 to 15 wt % of the combinedfeed. The oxygenate feed preferably comprises FAME, for example at least50 wt % FAME, and can consist essentially of FAME. In one process, thecombined feed contains not more than 5 wt % FAME.

The hydrotreatment in step b) can advantageously be carried out underrelatively mild conditions, so that no more than 86 wt % of the estersin the oxygenate feed stream are converted to hydrocarbons. In onepreferred embodiment, no more than 70 wt % of the esters in theoxygenate feed stream are converted to hydrocarbons.

In the embodiment of the invention where there are two hydrotreatmentreaction zones, the hydrotreatment in step b) is preferably carried outunder conditions so that no more than 50 wt %, more preferably no morethan 40 wt %, of the esters in the oxygenate feed stream are convertedto hydrocarbons in the first hydrotreatment reaction zone. In thatembodiment the hydrotreatment in the second reaction zone is preferablycarried out under conditions so that the product stream taken from thesecond hydrotreatment reaction zone contains less than 10 wt % esters,typically less than 5 wt % esters, and more preferably less than 1 wt %esters.

The hydrotreatment is typically carried out at temperatures in the rangeof from about 150° C. to about 430° C. and pressures of from about 0.1MPaa to about 25 MPaa.

Where the hydrotreatment is carried out in a single reaction zone, thetemperature can preferably range from about 200° C. to about 400° C.,more preferably from about 250° C. to about 380° C. However, in theembodiments of the invention where there are two stages ofhydrotreatment, the temperature in each reaction zone may be lower, as amilder hydrotreatment is carried out; in such embodiments, thetemperature can preferably range from about 150° C. to about 300° C.,more preferably from about 200° C. to about 300° C. Additionally oralternately, in certain two stage hydrotreatment embodiments, thetemperature in the first reaction zone can advantageously be lower thanthe temperature in the second reaction zone.

The hydrotreatment can advantageously be carried out at pressures offrom about 1 MPaa to about 20 MPaa. The hydrogen partial pressure in thehydrotreatment reaction zone(s) is (are) preferably from about 1 MPaa toabout 15 MPaa. The hydrogen used in any hydrotreatment process accordingto the invention may be a substantially pure, fresh feed, but it is alsopossible to use recycled hydrogen-containing feed from elsewhere in theprocess, or from the refinery, that may contain contamination fromby-products, preferably such that the chemical nature and/or theconcentration of the by-products in the hydrogen does not cause asignificant reduction (e.g., not more than a 10% reduction, preferablynot more than a 5% reduction) in the activity and/or lifetime of anycatalyst to which the hydrogen is exposed. The hydrogen treat gas ratiocan typically be in the range of about 50 Nm³/m³ (about 300 scf/bbl) toabout 1000 Nm³/m³ (about 5900 scf/bbl). In certain embodiments,typically when relatively milder hydrotreatment conditions are desired,the hydrogen treat gas ratio can be from about 75 Nm³/m³ (about 450scf/bbl) to about 300 Nm³/m³ (about 1800 scf/bbl) or from about 100Nm³/m³ (about 600 scf/bbl) to about 250 Nm³/m³ (about 1500 scf/bbl). Inother embodiments, typically when relatively harsher hydrotreatmentconditions are desired, the hydrogen treat gas ratio can be from about300 Nm³/m³ (about 1800 scf/bbl) to about 650 Nm³/m³ (about 3900 scf/bbl)or from about 350 Nm³/m³ (about 2100 scf/bbl) to about 550 Nm³/m³ (about3300 scf/bbl).

The hydrotreatment step(s) may be catalyzed, and suitable catalystsinclude those comprising one or more Group VIII metals and one or moreGroup VIB metals, for example comprising Ni and/or Co and W and/or Mo,preferably comprising a combination of Ni and Mo, or Co and Mo, or aternary combination such as Ni, Co, and Mo or such as Ni, Mo, and W. Theor each hydrotreatment catalyst is typically supported on an oxide suchas alumina, silica, zirconia, titania, or a combination thereof, oranother known support material such as carbon. Such catalysts are wellknown for use in hydrotreatment and hydrocracking.

A NiMo catalyst is preferably used to initiate olefin saturation at alower inlet temperature. Most units are constrained by a maximumoperating temperature, and large amounts of heat are released fromtreatment of biofeeds. Initiating olefin saturation at lower temperaturewith NiMo allows for longer cycle lengths (as the maximum temperaturewill be reached later) and/or permits processing of more biofeeds.

A CoMo catalyst is preferably used for lower hydrogen partial pressuredesulfurization and to slow down the kinetics of biofeed treatment.Spreading the exotherm out throughout the process by having such a loweractivity catalyst will reduce the number of hotspots (which decrease inefficiency of the unit, and potentially give rise to structural issuesif near reactor walls). At high hydrogen partial pressures, the use ofCoMo may also reduce the amount of methanation (e.g., CO+3H₂→CH₄+H₂Oand/or CO₂+4H₂→CH₄+2H₂O) that occurs, which helps to reduce hydrogenconsumption.

As used herein, the terms “CoMo” and “NiMo” refer to comprising oxidesof molybdenum and either cobalt or nickel, respectively, as catalyticmetals. Such catalysts may also optionally include supports and minoramounts of other materials such as promoters. By way of illustration,suitable hydrotreating catalysts are described, for example, in one ormore of U.S. Pat. Nos. 6,156,695, 6,162,350, 6,299,760, 6,582,590,6,712,955, 6,783,663, 6,863,803, 6,929,738, 7,229,548, 7,288,182,7,410,924, and 7,544,632, U.S. Patent Application Publication Nos.2005/0277545, 2006/0060502, 2007/0084754, and 2008/0132407, andInternational Publication Nos. WO 04/007646, WO 2007/084437, WO2007/084438, WO 2007/084439, and WO 2007/084471, inter alfa.

A combination of catalysts may be used in the first or in the second (orsubsequent) hydrotreatment reaction zones. These catalysts may bearranged in the form of a stacked bed. Alternatively, one catalyst maybe used in first hydrotreatment reaction zone and a second catalyst inthe second (or subsequent) hydrotreatment reaction zones. In a preferredarrangement the first hydrotreatment reaction zone comprises a stackedbed of NiMo catalyst, followed by a CoMo catalyst. The second reactionzone preferably comprises a CoMo catalyst. Nevertheless, in alternatearrangements stacked bed arrangements, the NiMo catalyst in the firsthydrotreatment zone may be substituted with a catalyst containing Ni andW metals or a catalyst containing Ni, W, and Mo metals.

The hydrotreatment may be conducted at liquid hourly space velocities(LHSV) of from about 0.1 hr⁻¹ to about 10 hr⁻¹, for example from about0.3 hr⁻¹ to about 5 hr⁻¹, preferably from about 0.5 hr⁻¹ to about 5hr⁻¹. In the embodiment of the invention where there are two stages ofhydrotreatment, the conditions in either or each reaction zone (or eachreactor, where the reaction zones are in separate reactors) may bemilder, and as indicated above this may be achieved by using lowertemperatures. Alternatively or in addition, the LHSV may be increased toreduce severity. In such an embodiment, the LHSV is preferably fromabout 1 hr⁻¹ to about 5 hr⁻¹.

It is believed to be within the competence of one skilled in the art toselect an appropriate catalyst, and then determine the specificconditions within the above-mentioned ranges under which thehydrotreatment according to the invention may be carried out, so thathydrodesulfurization of the hydrocarbon feed and conversion of theoxygenate feed to hydrocarbons can be achieved, e.g., withoutsignificant loss of hydrocarbons boiling in the diesel range due tounwanted hydrocracking.

Following hydrotreatment, whether in a single hydrotreatment step or ina sequence of two or more hydrotreatment steps, a hydrotreated productstream is recovered from the hydrotreatment and a hydrocarbon productstream suitable for use as fuel can then be separated from it. Thehydrotreated product stream may be subjected to conventional separationprocesses to achieve this; for example, flash separation to remove lightends and gases, and fractionation to isolate hydrocarbons boiling in thediesel fuel range.

In addition, the hydrotreated product stream may be subjected tooptional hydroisomerization over an isomerization catalyst to improvethe properties of the final product, such as the cold flow properties.

In the embodiments of the invention where the hydrotreatment of anoxygenate feed stream comprising olefinic unsaturations and thehydrocarbon feed stream are carried out in two or more hydrotreatmentreaction zones, the hydrotreatment is preferably conducted to split heatrelease between the two reaction zones. For example, in the firsthydrotreatment reaction zone the olefins may be saturated, and themethyl or ethyl ester groups removed along with some oxygen removal, andthen in the second hydrotreatment reactor the conversion to hydrocarbonssuitable for use as fuel is completed. This enables each stage to becarried out under relatively milder conditions and with better controlof heat release than would a single stage hydrotreatment to achievesimilar hydrocarbon conversion.

The first hydrotreated product stream removed from the firsthydrotreatment reaction zone may optionally be cooled before it ishydrotreated within the second hydrotreatment reaction zone usingconventional means, such as heat exchangers or quench gas treatment.Heat recovered in this way may be used to preheat feed at other pointsin the process, such as the oxygenate feed or the hydrocarbon feed tothe first reaction zone.

A further option is to pass the first hydrotreated product streamthrough a separator to separate out any light ends, CO, CO₂, or waterbefore it is passed into the second reaction zone. Such removal of theCO and water may improve catalyst activity and cycle length.

The hydrocarbon product stream recovered from step d) may be used asfuel, such as diesel fuel, heating oil, or jet fuel, either alone orcombined with other suitable streams. A preferred use of the hydrocarbonproduct stream is as diesel fuel and it may be sent to the diesel fuelpool. It may also be subjected to further convention treatments,including the addition of additives to enhance the performance, e.g., asa diesel fuel.

This invention extends to a fuel, such as diesel fuel, heating oil, orjet fuel, when prepared by the process as described herein.

In one embodiment, the product hydrocarbon stream recovered from step d)can comprise at least 90 wt % saturated hydrocarbons (preferably atleast 93 wt % or at least 95 wt %; typically up to about 99.9 wt %, upto about 99.5 wt %, up to about 99 wt %, or up to about 98 wt %), lessthan 1 wt % ester-containing compounds (for example less than 0.5 wt %,less than 0.2 wt %, less than 0.1 wt %, less than 500 wppm, less than200 wppm, or less than 100 wppm; if any ester-containing compounds aredetectable, they can be present in amounts as low as 100 wppb, 200 wppb,500 wppb, 1 wppm, 2 wppm, 5 wppm, or 10 wppm), less than 1 wt %acid-containing compounds (for example less than 0.5 wt %, less than 0.2wt %, less than 0.1 wt %, less than 500 wppm, less than 200 wppm, lessthan 100 wppm, less than 75 wppm, less than 50 wppm, or less than 25wppm; if any acid-containing compounds are detectable, they can bepresent in amounts as low as 100 wppb, 200 wppb, 500 wppb, 1 wppm, 2wppm, or 5 wppm), and not more than 10 wppm sulfur-containing compounds,based on the total weight of the product hydrocarbon stream. In thisembodiment, the product hydrocarbon stream can be used as, and/or can beused as a blend component in combination with one or more otherhydrocarbon streams, to form a diesel fuel, a jet fuel, a heating oil,or a portion of a distillate pool.

In another embodiment, where there are at least first and secondhydrotreatment reaction zones, the partially converted firsthydrotreated product stream from step (b)(ii) can comprise from about 30wt % to about 60 wt % of compounds containing only hydrogen and carbonatoms, at least about 4 wt % trans-esterified (i.e., containing thealkyl group from the alcohol, preferably methyl) ester-containingcompounds, at least about 2 wt % acid-containing compounds that arefully saturated, and at least about 0.3 wt % alkyl alcohols, based onthe total weight of the partially converted first hydrotreated productstream.

By way of illustration only, the invention is now described in moredetail by reference to the accompanying drawings which show certainpreferred or alternative aspects of the invention.

In the apparatus depicted in the FIGURE, the combined oxygenate feedstream and hydrocarbon feed stream are fed by line 1 into a reactor 3which forms a first hydrotreatment reaction zone. Hydrogen is separatelyfed via line 2 into reactor 3.

After hydrotreatment in reactor 3, a first hydrotreated product stream 4is fed to a high pressure separator 5, from the head of which a lightstream is fed via line 7 to a low pressure separator 8. Light ends, andgases including H₂S, NH₃, CO and CO₂ are taken from the low pressureseparator 8 via line 11 to a scrubber (not shown).

From the base of the high pressure separator 5 and from the low pressureseparator 8, streams are fed by lines 6 and 9 respectively, to anoptional intermediate feed surge tank 10 and then by line 12 into asecond reactor 13 which forms a second hydrotreatment reaction zone.Fresh (or recycled) hydrogen is introduced into reactor 13 through line14.

As an alternative to the arrangement shown in the FIGURE, a single stageof separation could replace separators 5 and 8.

After further hydrotreatment in reactor 13, a second hydrotreatedproduct stream 15 is fed to another high pressure separator 16, from thehead of which a light stream is fed via line 17 to another low pressureseparator 18. Offgas is taken from the low pressure separator 18 vialine 19 to a scrubber (not shown).

From the base of the high pressure separator 16 and from the lowpressure separator 18, hydrocarbon streams suitable for use as dieselfuel are fed by lines 20 and 21 respectively, to the diesel pool 22.

Again, as an alternative to the arrangement shown in the FIGURE, asingle stage of separation could replace separators 16 and 18.

Additionally or alternately, the present invention includes thefollowing embodiments.

Embodiment 1

A process for producing a hydrocarbon stream suitable for use as fuelfrom carboxylic esters, which process comprises the steps of: a) feedingto a hydrotreatment reaction zone (i) an oxygenate feed streamcomprising one or more methyl or ethyl esters of carboxylic acids, and(ii) a hydrocarbon feed stream; b) contacting the feed streams withinthe hydrotreatment reaction zone with a gas comprising hydrogen underhydrotreatment conditions until not more than 86 wt % of the esters inthe oxygenate feed stream are converted to hydrocarbons; c) removing ahydrotreated product stream; and d) separating from the hydrotreatedproduct stream a hydrocarbon stream suitable for use as fuel.

Embodiment 2

A process for producing a hydrocarbon stream suitable for use as fuelfrom carboxylic esters, which process comprises the steps of: a) feedingto a first hydrotreatment reactor an oxygenate feed stream comprisingone or more esters of carboxylic acids, and a hydrocarbon feed stream;b) (i) contacting the feed streams within the first hydrotreatmentreaction zone with a gas comprising hydrogen under hydrotreatmentconditions until not more than 86 wt % of the esters in the oxygenatefeed stream are converted to hydrocarbons, (ii) removing from the firsthydrotreatment reaction zone a first hydrotreated product stream, and(iii) contacting the first hydrotreated product stream within at least asecond hydrotreatment reaction zone with a gas comprising hydrogen underhydrotreatment conditions until at least 90 wt % of the esters in theoxygenate feed stream are converted to hydrocarbons; c) removing fromthe second hydrotreatment reaction zone a second hydrotreated productstream; and d) separating from the second hydrotreated product stream ahydrocarbon stream suitable for use as fuel.

Embodiment 3

A process according to embodiment 2, wherein the oxygenate feed streamcomprises one or more methyl and/or ethyl esters of carboxylic acids,preferably methyl esters, and/or is derived from a plant oil, an animaloil or fat, algae, waste oil, or a combination thereof.

Embodiment 4

A process according to any of the preceding embodiments, wherein theoxygenate feed stream is obtained by transesterification of C₈ to C₃₆carboxylic esters with an alcohol, preferably methanol, in the presenceof a base catalyst.

Embodiment 5

A process according to any of the preceding embodiments, wherein thehydrocarbon feed is a middle distillate, a gas oil fraction, a vacuumgas oil, or a combination thereof.

Embodiment 6

A process according to any of the preceding embodiments, wherein theoxygenate feed comprises from about 1 wt % to about 15 wt % of thecombined feed to the hydrotreatment reaction zone in step a).

Embodiment 7

A process according to embodiment 6, wherein the combined feed streamsto the hydrotreatment reaction zone in step a) comprise not more than 5wt % FAME.

Embodiment 8

A process according to any of the preceding embodiments, wherein thehydrotreatment in step b) is carried out under relatively mildconditions so that no more than 70 wt % of the esters in the oxygenatefeed stream are converted to hydrocarbons.

Embodiment 9

A process according to any of the preceding embodiments, wherein thehydrotreatment in step b) is carried out at a temperature from about150° C. to about 430° C. and a pressure from about 0.1 MPaa to about 25MPaa, preferably at a temperature from about 250° C. to about 380° C.and a pressure from about 1 MPaa to about 15 MPaa.

Embodiment 10

A process according to embodiment 2 or embodiment 3, wherein thehydrotreatment in step b) is carried out under conditions so that nomore than 50 wt %, more preferably no more than 40 wt %, of the estersin the oxygenate feed stream are converted to hydrocarbons in the firsthydrotreatment reaction zone.

Embodiment 11

A process according to any of embodiments 2, 3, or 10, wherein thetemperature in each reaction zone is from about 150° C. to about 300°C., preferably from about 200° C. to about 300° C., the pressure in eachreaction zone is from about 1 MPaa to about 15 MPaa, and/or the LHSV ineach reaction zone is from 0.3 hr⁻¹ to 5 hr⁻¹.

Embodiment 12

A process according to any of the preceding embodiments, wherein the oreach hydrotreatment is catalyzed using a catalyst comprises two or moreof Ni, Co, W, and Mo, optionally supported on alumina, silica, zirconia,titania or carbon, preferably wherein the or each catalyst comprises acombination of Ni and Mo, or Co and Mo, and optionally wherein the oreach reaction zone comprises a stacked bed of NiMo catalyst, followed bya CoMo catalyst.

Embodiment 13

A process according to any of the preceding embodiments, wherein thehydrotreated product stream is subjected to hydroisomerization over anisomerization catalyst to improve cold flow properties of thehydrocarbon stream suitable for use as fuel.

Embodiment 14

A process according to any of embodiments 2, 3, 10, 11, or 12, whereinthe first hydrotreated product stream removed from the firsthydrotreatment reaction zone is cooled and/or passed through a separatorto remove light ends, CO, CO₂, and water before being hydrotreatedwithin the second hydrotreatment reaction zone.

Embodiment 15

A process according to any of the preceding embodiments wherein thehydrocarbon stream recovered after step d) is a diesel fuel.

The following Examples provide further illustration of aspects of theinvention without limiting the scope of the invention.

Examples 1-7

An oxygenate feed comprising FAME was prepared by transesterification ofrapeseed oil. The oxygenate feed had the following composition, set outin Table 1 below.

TABLE 1 Wt % Feed Component 4.5% Methyl ester of C ¹⁶ saturated acid1.6% Methyl ester of C ¹⁸ saturated acid 62.1% Methyl ester of C ¹⁸ acidwith 1 olefin bond 19.3% Methyl ester of C ¹⁸ acid with 2 olefin bonds10.0% Methyl ester of C ¹⁸ acid with 3 olefin bonds 0.5% Methyl ester ofC ²⁰ saturated acid

This oxygenate feed was combined with a hydrocarbon feed comprising alight gas oil (LGO) in various proportions. The proportions were chosento demonstrate the effect of hydrotreatment, and do not necessarilyreflect typical proportions likely to be chosen for diesel fuels, e.g.,for sale in the short term in Europe. The combined feeds are shown inTable 2 below.

TABLE 2 40% bio 45% bio 50% bio wt % wt % wt % Component  1.81  2.03 2.26 Methyl ester of C ¹⁶ saturated acid  0.64  0.72  0.80 Methyl esterof C ¹⁸ saturated acid 24.85 27.95 31.06 Methyl ester of C ¹⁸ acid with1 olefin bond  7.73  8.70  9.67 Methyl ester of C ¹⁸ acid with 2 olefinbonds  4.01  4.51  5.01 Methyl ester of C ¹⁸ acid with 3 olefin bonds 0.20  0.23  0.25 Methyl ester of C ²⁰ saturated acid 60.00 55.00 50.00Hydrocarbons from LGO

These combined feeds were then hydrotreated in single and double reactorarrangements. In Examples 1-5 the combined feeds were subjected tohydrotreatment, carried out in a single reactor containing two catalystsas a stacked bed. The first catalyst was a NiMo catalyst. The secondcatalyst was a CoMo catalyst. Examples 6 and 7 were hydrotreated in twosuccessive reactors. The first reactor was the same as used in Examples1-5, and the subsequent reactor contained only the CoMo catalyst. Thetables below show the conditions in each stage, as well as the analysisof the hydrotreated product form each stage.

The conditions used in the Examples are set out in Table 3 below, thecomposition of the hydrotreated products obtained are set out in Table 4below, and the conversion figures are set out in Table 5 below.

TABLE 3 Example 1 2 3 4 5 6 7 No. of Reactors 1 1 1 1 1 1 2 1 2 CombinedFeed 40% 40% 40% 45% 50% 50% 50% 50% 50% bio bio bio bio bio bio bio biobio Inlet H₂ Partial 2.76 4.83 6.9 10.35 13.8 13.8 13.8 13.8 13.8Pressure, MPaa First Reactor ° C. 271.9 272.6 273.4 274.7 275.7 223.8 —223.9 — Second Reactor ° C. — — — — — — 251.1 — 251.1 Treat Gas Ratio1370 1370 1370 1250 1250 1260 1260 1260 1260 H₂ scf/bbl LHSV, hr⁻¹ 1.51.5 1.5 1.5 1.5 3 3 3 3 Outlet H₂ Partial 2.08 3.65 5.26 6.69 7.44 12.7812.78 12.78 12.78 Pressure, MPaa

TABLE 4 wt % in product/Ex. # 1 2 3 4 5 6 7 Methyl ester of C₁₆  0.4 0.3  0.2  0.2  0.2  1.9  1.4  1.8  1.4 saturated acid Methyl ester ofC₁₈  4.2  4.1  3.6  3.5  3.2 20.6 20.0 20.5 20.5 saturated acid Methylester of C₁₈ acid  4.0  2.9  1.5  1.1  0.6 14.2  7.0 14.8  7.0 with 1olefin bond 1-octadecanol  0.1  0.2  0.4  0.7  1.3  0.7  0.9  0.7  0.9Methyl ester of C₂₀  0.1  0.1  0.1  0.1  0.1  0.5  0.5  0.5  0.5saturated acid C₁₆ saturated acid  0.4  0.2  0.2  0.1  0.1  0.1  0.2 0.1  0.2 C₁₈ saturated acid  4.9  4.8  4.3  4.3  3.9  2.7  5.8  2.3 6.0 C₁₈ acid with 1 olefin  1.1  0.7  0.4  0.2  0.0  0.2  0.1  0.2  0.2bond Hydrocarbons 84.7 86.5 89.2 89.6 90.7 58.1 63.8 58.1 62.4

TABLE 5 Example 1 2 3 4 5 6 7 Overall conversion of FAME, wt % C₁₆ 80 8187 89 92 17 39 20 37 C₁₈ 78 81 86 89 92 25 42 24 41 Conversion of FAMEto carboxylic acid, wt % C₁₆ 22 12 9 7 6 4 9 3 9 C₁₈ 16 15 13 12 10 8 167 17 Conversion of FAME to hydrocarbons, wt % C₁₆ 58 69 78 82 86 13 3017 28 C₁₈ 62 66 74 77 82 18 26 18 24

From these results it can be seen that the use of two reactors helps tospread heat release out between the reactors, potentially with heatexchangers to utilize heat integration techniques. This may allow for alarger amount of biofeeds to be treated. It also enables CO, to beremoved before the second reactor, so reducing the hydrodesulfurizationinhibition of the CoMo catalyst in the later stages. The arrangement mayalso allow the process to run at lower temperatures to meet a givensulfur targets, such as 10 ppm sulfur required for ultra low sulfurdiesel (ULSD), by adjusting the temperatures and sulfur slip from thetwo reactors.

1. A process for producing a hydrocarbon stream suitable for use as fuelfrom carboxylic esters, which process comprises the steps of: a) feedingto a hydrotreatment reaction zone (i) an oxygenate feed streamcomprising one or more methyl or ethyl esters of carboxylic acids, and(ii) a hydrocarbon feed stream; b) contacting the feed streams withinthe hydrotreatment reaction zone with a gas comprising hydrogen underhydrotreatment conditions until not more than 86 wt % of the esters inthe oxygenate feed stream are converted to hydrocarbons; c) removing ahydrotreated product stream; and d) separating from the hydrotreatedproduct stream a hydrocarbon stream suitable for use as fuel.
 2. Aprocess according to claim 1, wherein the oxygenate feed stream isderived from a plant oil, an animal oil or fat, algae, waste oil, or acombination thereof.
 3. A process according to claim 1, wherein theoxygenate feed stream is obtained by transesterification of C₈ to C₃₆carboxylic esters with an alcohol in the presence of a base catalyst. 4.A process according to claim 3, wherein the oxygenate feed streamcomprises fatty acid methyl esters.
 5. A process according to claim 1,wherein the hydrocarbon feed is a middle distillate, a gas oil fraction,a vacuum gas oil, or a combination thereof.
 6. A process according toclaim 4, wherein the oxygenate feed comprises from about 1 wt % to about15 wt % of the combined feed to the hydrotreatment reaction zone in stepa).
 7. A process according to claim 6, wherein the combined feed streamsto the hydrotreatment reaction zone in step a) comprise not more than 5wt % FAME.
 8. A process according to claim 1, wherein the hydrotreatmentin step b) is carried out under relatively mild conditions so that nomore than 70 wt % of the esters in the oxygenate feed stream areconverted to hydrocarbons.
 9. A process according to claim 1, whereinthe hydrotreatment in step b) is carried out at a temperature from about150° C. to about 430° C. and a pressure from about 0.1 MPaa to about 25MPaa.
 10. A process according to claim 9, wherein the hydrotreatment instep b) is carried out at a temperature from about 250° C. to about 380°C. and a pressure from about 1 MPaa to about 15 MPaa.
 11. A processaccording to claim 1, wherein the reaction zone has an LHSV from 0.3hr⁻¹ to 5 hr⁻¹.
 12. A process according to claim 1, wherein thehydrotreatment is catalyzed using a catalyst comprising two or more ofNi, Co, W, and Mo, optionally supported on alumina, silica, zirconia,titania, or carbon.
 13. A process according to claim 1, wherein thehydrotreated product stream is subjected to hydroisomerization over anisomerization catalyst to improve cold flow properties of thehydrocarbon stream suitable for use as fuel.
 14. A process according toclaim 1, wherein the hydrocarbon stream recovered after step d) is adiesel fuel.
 15. A process for producing a hydrocarbon stream suitablefor use as fuel from carboxylic esters, which process comprises thesteps of: a) feeding to a first hydrotreatment reactor an oxygenate feedstream comprising one or more esters of carboxylic acids, and ahydrocarbon feed stream; b) (i) contacting the feed streams within thefirst hydrotreatment reaction zone with a gas comprising hydrogen underhydrotreatment conditions until not more than 86 wt % of the esters inthe oxygenate feed stream are converted to hydrocarbons, (ii) removingfrom the first hydrotreatment reaction zone a first hydrotreated productstream, and (iii) contacting the first hydrotreated product streamwithin at least a second hydrotreatment reaction zone with a gascomprising hydrogen under hydrotreatment conditions until at least 90 wt% of the esters in the oxygenate feed stream are converted tohydrocarbons; c) removing from the second hydrotreatment reaction zone asecond hydrotreated product stream; and d) separating from the secondhydrotreated product stream a hydrocarbon stream suitable for use asfuel.
 16. A process according to claim 15, wherein the oxygenate feedstream comprises one or more methyl and/or ethyl esters of carboxylicacids.
 17. A process according to claim 15, wherein the oxygenate feedstream is derived from a plant oil, an animal oil or fat, algae, wasteoil, or a combination thereof.
 18. A process according to claim 15,wherein the oxygenate feed stream is obtained by transesterification ofC₈ to C₃₆ carboxylic esters with an alcohol in the presence of a basecatalyst.
 19. A process according to 17, wherein the oxygenate feedstream comprises fatty acid methyl esters.
 20. A process according toclaim 15, wherein the hydrocarbon feed is a middle distillate, a gas oilfraction, a vacuum gas oil, or a combination thereof.
 21. A processaccording to claim 19, wherein the oxygenate feed comprises from about 1wt % to about 15 wt % of the combined feed to the hydrotreatmentreaction zone in step a).
 22. A process according to claim 22, whereinthe combined feed streams to the hydrotreatment reaction zone in step a)comprise not more than 5 wt % FAME.
 23. A process according to claim 15,wherein the hydrotreatment in step b) is carried out under relativelymild conditions so that no more than 70 wt % of the esters in theoxygenate feed stream are converted to hydrocarbons.
 24. A processaccording to claim 15, wherein the hydrotreatment in step b) is carriedout at a temperature from about 150° C. to about 430° C. and a pressurefrom about 0.1 MPaa to about 25 MPaa.
 25. A process according to claim24, wherein the hydrotreatment in step b) is carried out at atemperature from about 250° C. to about 380° C. and a pressure fromabout 1 MPaa to about 15 MPaa.
 26. A process according to claim 17,wherein the hydrotreatment in step b) is carried out under conditions sothat no more than 50 wt %, more preferably no more than 40 wt %, of theesters in the oxygenate feed stream are converted to hydrocarbons in thefirst hydrotreatment reaction zone.
 27. A process according to claim 26,wherein the temperature in each reaction zone is from about 150° C. toabout 300° C., and the pressure in each reaction zone is from about 1MPaa to about 15 MPaa
 28. A process according to claim 15, wherein theor each reaction zone has an LHSV from 0.3 hr⁻¹ to 5 hr⁻¹.
 29. A processaccording to claim 15, wherein each hydrotreatment is catalyzed using acatalyst comprising two or more of Ni, Co, W, and Mo, optionallysupported on alumina, silica, zirconia, titania, or carbon.
 30. Aprocess according to claim 29, wherein each catalyst comprises acombination of Ni and Mo, or Co and Mo.
 31. A process according to claim29, wherein each reaction zone comprises a stacked bed of NiMo catalyst,followed by a CoMo catalyst.
 32. A process according to claim 15,wherein the hydrotreated product stream is subjected tohydroisomerization over an isomerization catalyst to improve cold flowproperties of the hydrocarbon stream suitable for use as fuel.
 33. Aprocess according to claim 15, wherein the first hydrotreated productstream removed from the first hydrotreatment reaction zone is cooledbefore being hydrotreated within the second hydrotreatment reactionzone.
 34. A process according to claim 15, wherein the firsthydrotreated product stream is passed through a separator to removelight ends, CO, CO₂, and water before being hydrotreated within thesecond hydrotreatment reaction zone.
 35. A process according to claim15, wherein the hydrocarbon stream recovered after step d) is a dieselfuel.